In recent years, steps have been taken to minimize the size of films in order to improve the portable use of cameras by miniaturization thereof. However, minimization of the films brings about deterioration of quality of prints, which is well known. Namely, production of prints having the same size requires a larger magnification of enlargement, and, consequently, graininess and sharpness of the printed images become inferior. Accordingly, it is necessary to improve graininess, resolving power and sharpness of films in order to obtain good prints using miniaturized cameras. It is, of course, desired to use films which give clear color.
Improvement of the graininess or granularity can be carried out by increasing the number of silver halide particles as described in T. H. James, The Theory of the Photographic Process, 4th Ed., pp. 620 and 621, and by diffusing dyes formed by color development. However, in order to increase the number of silver halide particles while maintaining the photographic sensitivity, the amount of silver coated increases resulting in deterioration of resolving power, and it is disadvantageous with respect to cost and photographic properties.
Further, with attempts of improving granularity by diffusion of dyes, when non-diffusible couplers which form a dye of such mobility that controlled image smearing occurs are used as described in, for example, British Pat. No. 2,083,640 A, the so-called RMS granularity (RMS granularity has been described in T. H. James, The Theory of the Photographic Process, 4th Ed., p. 619) is remarkably improved. However, since arrangement of silver halide particles and development probability are brought in random processes, the dye diffuses and mixes with adjacent dyes depending upon the degree of diffusibility, whereby overlap of dye clouds becomes large and, consequently, huge dye clouds are randomly formed. It is very visually unpleasant and the granularity sometimes seems to be rather deteriorated. Further, as naturally expected, sharpness deteriorates because of dye diffusion.
On the other hand, in order to improve the sharpness, it has been known to use compounds which form a dye and release a development inhibitor by coupling with an oxidation product of the color developing agent, as described in U.S. Pat. Nos. 3,148,062 and 3,227,554, and compounds which release a development inhibitor by coupling with an oxidation product of the color developing agent but do not form a dye, as described in U.S. Pat. No. 3,632,345 (hereinafter, both compounds are referred to as "DIR compounds"). However, if the amount of DIR compounds added is increased, the coloring property deteriorates, and, consequently, the coating amount of silver halide or couplers increases in order to compensate for the above fault resulting in deterioration of the resolving power in a high space frequency area. Accordingly, there is a limit in improvement of sharpness by this process.
Further, if the coating amount of silver is reduced, light scattering of the emulsion layer becomes small and improvement of sharpness can be attained. However, it is obvious that, when the coating amount of silver is reduced, the number of development active points is reduced causing deterioration of granularity.
As described above, improvement of granularity and sharpness has been attempted in this field of the art as a subject for study, but sufficient results have not been obtained yet. In many cases, the means of improvement have an inverse relationship to one another, as described above.